Fibrils

ABSTRACT

A process for preparing carbon fibrils by contacting a source of carbon with a supported catalyst that includes at least one multivalent transition metal having a size of about 35 to 700 A deposited on an inorganic substrate having a size of up to about 400 microns.

[0001] This application is a continuation-in-part of application Ser.No. 149,573, filed Jan. 8, 1988, application Ser. Nos. 872,215, 871,675and 871,676 all filed Jun. 6, 1986 and application Ser. No. 678,701,filed Dec. 6, 1984, now U.S. Pat. No. 4,663,230, all of which areincorporated herein in their entirety by reference.

[0002] This invention relates to fibrils. It more particlarly refers tocarbon/graphite fibrils and to an improved process for producing such.Carbon fibrils as used herein means graphitic fibrils having highsurface area, high Young's modulus of elasticity and high tensilestrength which are grown catalytically from available sources of carbon.

BACKGROUND OF THE INVENTION

[0003] It has been known for some time that one could make fibrils bydecomposing various carbon contributing molecules, such as lighthydrocarbons, in contact with a suitable metal catalyst, such as forexample iron alone or in combination with other metals. In the past, thefibrils which have been made have been somewhat thicker than desirableand/or have been burdened with an overcoat of thermally depositedgenerally amorphous carbon which tended to reduce the desirable physicalproperties thereof or have been made in poor yields. Prior workers havesought to ameliorate the disadvantages of the amorphous carbonovercoating by subjecting the finished fibril to a very high temperaturegraphitizing treatment whereby generally rendering the fibrils ofsubstantially greater cross sectional consistency from both acomposition and a crystallinity point of view.

[0004] It is obvious that the improved fibril properties engendered bythis high temperature graphitization process are expensive, because hightemperature treatments are expensive. Additionally, such graphitizedfibrils may still be too thick for many purposes because, graphitizingdoes not significantly reduce the fibril diameter. Thus, it is desiredto produce high yields of high quality fibrils, preferably thin fibrils,which, in a preferred aspect of this invention, do not need postproduction graphitization.

SUMMARY OF THE INVENTION

[0005] More particlarly refers to carbon/graphite fibrils and to animproved process for producing such. Fibrils are made according to thisinvention in a high temperature, catalytic process. The Fibril can bemade of a variety of materials, e.g. carbon, silicon nitride, siliconcarbide, etc. In one important embodiment, such fibrils have the atomsin their composition relatively ordered at their outer surfaces as theyare made by this process. Thus, it can be said that this processpreferably directly produces a product having a relatively crystallineouter region for substantial portions of its length and may have innerregions where its atoms are less ordered. It may, and often does, evenhave a hollow region axially positioned along substantial portions ofits length.

[0006] Fibrils according to this invention are characterized by smalldiameters, e.g. about 35 to 70 nanometers and high L/D up to about 100and even more.

[0007] Where the preferred structure described above is produced, it issuitably produced directly in the fibril forming process without furtherprocessing being required.

[0008] Where the fibrils of this invention are to be made of carbon,such can be produced in quite high yields. In this embodiment, asuitable source of carbon may be a hydrocarbonaceous materialillustrated by: methane, ethane, propane, butane, benzene, cyclohexane,butene, isobutene, ethylene, propylene, acetylene, toluene, xylene,cumene, ethyl benzene, naphthalene, phenanthrene, anthracene,formaldehyde, acetaldehyde, acetone, methanol, ethanol, carbon monoxide,other similar materials, and mixtures of two (2) or more thereof. Suchfeed is contacted with a suitable, catalyst at elevated, fibril formingtemperatures for a time sufficient to cause graphitic carbon fibrils togrow.

[0009] It is within the scope of this invention to provide anon-hydrocarbonaceous gas along with the carbon contributing reactant.Such gas might for example be hydrogen or carbon monoxide. Inertdiluents are also suitable.

[0010] The temperature of the process of this invention can vary widelydepending upon the nature of the carbon source being used, however, forbest results, it should be kept below the thermal decompositiontemperature thereof. In the case of using a mixture of such carbonsources, the operating temperature should be maintained below thethermal decomposition temperature of the most temperature-sensitivecarbon source in the system. Temperatures in the range of 500 to 1500°C. may be found to be generally usable, depending on the carbon sourceused, preferably between about 600 and 900° C.

[0011] Subatmospheric, atmospheric and/or super atmospheric pressuresmay be used as dictated by other processing considerations. It has beenfound that it is desirable to provide the carbon source in the vaporstate, and thus, the pressure should not be so high as to cause thecarbon source to be in the liquid state under fibril forming temperatureconditions. Further, it is desirable although not essential to provide asuitable gaseous diluent, such as hydrogen or inert gases, for example,nitrogen.

[0012] It is preferred that the system as a whole be non-oxidizingwherefor preferably avoiding the presence of oxygen if practical. Smallamounts of these materials can be tolerated. It should be understoodthat the existence of oxidizing conditions, at the elevated temperaturesoperative for this process, will cause oxidation of the carbon sourceand therefor reduce the amount of carbon from such source which isavailable for conversion into fibrils as desired.

[0013] It may be desirable to provide suitable heat to this reactionsystem where and when needed. Temperature of different parts of thereactor zone may be suitably controlled to different temperatures andthis is easily accomplished by using electrical resistance heating.However in larger scale industrial practice, electric resistance heatingmay sometimes be economically replaced by direct heating, such as forexample by burning some of the carbon contributing feed to raise thetemperature of the remainder of the feed, or by feeding the catalyst orthe carbon contributing feed, or the diluent into the system at asufficiently elevated temperature such that direct heat exchange of thecomponent with each other will cause the fibril forming reaction toproceed as desired.

[0014] The nature of the catalyst seems to have a significant effectupon the yield of fibrils produced according to this invention. It isknown to use iron group metals such as iron, cobalt or nickel tocatalyze the conversion of carbon contributing compounds to fibrils, andsuch metals are within the scope of this invention. In addition, manyother multivalant transition metals, including lanthanides, appear to beoperative. Particularly useful catalytic metals include inter alia:iron, molybdenum cobalt, nickel, platinum, palladium, vanadium, andchromium. Of specific interest in this process are certain combinationsof transition metals. Particularly useful combinations include iron andmolybdenum, iron and chromium, copper and nickel, iron and platinum,iron and tin, iron and nickel, iron and manganese, and iron and cerium.

[0015] The yield of fibrils produced according to the practice of thisinvention appears to be related to the physical state of the catalystused to produce such. According to this invention, it is important thatthe multivalent transition metal fibril forming catalyst be present on asuitable substrate as relatively discrete catalytic sites, each about 35to 700A preferably 60 to 300A in size during fibril formation. Theserelatively discrete catalytic sites are produced by suitably applyingthe transition metal (in an appropriate state) to a substrate, suitablyan inorganic substrate material which can include carbon/graphite.

[0016] The size of the substrate particle is a matter of some importancedependent upon the engineering of the process itself. For example, ifthe fibril formation is to take place in a fluid bed type of reactionzone, the substrate particle size will suitably be less than about 400microns. If the fluid bed is an evullient bed of catalyst particles,particle sizes of about 50 to 300 microns have been found to bepreferable. If the fluid bed is an evullient bed of fibrils containingsmall amounts of catalyst particles, i.e. up to about ten percent, theseshould preferably have a size of about 1 to 100 microns. If the fluidbed is a transport bed, either up flow or down flow, the catalystcarrying particles will suitably be less than about 10 microns,preferably less than about one micron.

[0017] It has been found that depositing one or more suitable transitionmetals on small particle substrates produces a catalyst well suited touse in this invention. The substrate is a material which canconveniently withstand the rigors of fibril formation conditions, e.g.temperatures of about 500 to 1500° C. Suitable substrates includecarbon, graphite, inorganic oxides, etc. The particular substrate willbe matched to the particular transition metal(s) catalyst such that themetal is bound strongly enough to retard migration and agglomeration butnot so strongly as to prevent or retard the transition metal fromcatalyzing fibril formation. Illustrative, inorganic oxides includealumina, silica, magnesia, silicates, aluminates, spinels etc. Mixturescan be used.

[0018] Thus, very small particle iron, such as might be produced bydecomposition of iron compounds, can be deposited on very small particlealumina, e.g. fumed alumina having particle sizes of no larger thanabout 100 mesh. These alumina particles may be made up of individualcrystallites which are on the order of about 50 to 200 A, whichagglomerate to form particles having substantial available surface areasufficient to receive deposits of appropriately sized transition metalcatalyst.

[0019] The substrate particles are suitably less than about 300 microns.They may be less than 1 micron in transport bed use. It appears that thetransition metal reacts with the substrate crystallites such as to bondthe metal to the substrate and fix its position, so as to prevent orretard catalyst agglomeration, at least for so long as it takes tocontact the supported transition metal with the suitable carbon sourceat appropriate reaction conditions. Upon contact, the carbon sourceseems to pyrolyze on the catalytic site and the desirable morphologyfibril grows therefrom.

[0020] As noted, the state of the transition metal catalyst site duringfibril formation is important to the practice of this invention.Sometimes, it appears that this desirable catalytic site state as wellas the state of the substrate carrier therefore is changing during thewhole process hereof. Thus, the catalytic sites may agglomerate ordisperse to some extent during the period from introduction into thereaction zone until the fibrils made by the process are recovered. Atthe time the fibrils are recovered, particles of transition metalcatalyst which are sometimes recovered with the fibrils are of about 35to 700 A, preferably 60to 300A in size. Thus, it is believed that thesize of the active catalyst site during fibril formation issubstantially comparable to the diameter of the fibril being formed.

[0021] It appears that as fibril formation takes place, active catalystsites become catalytically expended and need to be replaced.Additionaly, it has been found that the fibril forming process is moreefficient and capable of better control if the catalyst is added to thereaction zone intermittently or continuously over substantially theentire course of the reaction, or at least a substantial portionthereof. It is possible that the catalyst containing substrate of thisinvention may ablate with use. That is, when a fibril is formed on aparticular catalytic site, that fibril and its associated site may breakoff from the substrate, with or without some of the substrate, therebyexposing further catalytic sites which were previously inside thesubstrate particle. Thus, periodic or continuous addition of freshcatalyst is desirable

[0022] Thus, according to this invention, the fibril forming processhereof is preferably substantially continuous in that a suitable sourceof carbon, with or without carrier gas, and catalyst containingparticles are continuously or intermittently fed to a reaction zonemaintained at a fibril forming temperature appropriate to the carbonsource being used; while fibril product, usually admixed with theremnants of the catalyst and sometimes substrate as well, arecontinuously or intermittently recovered.

[0023] The transition metal may be deposited on the substrate by anycommonly used technique for accomplishing such deposition. Vapordeposition, sputtering and impregnation may all be suitable. Inparticular, it has been found to be expeditious to form a water solutionor dispersion of the desired metal or metals, mix the water phase withappropriately sized substrate, and then precipitate the metal(s) ontothe substrate, e.g. by evaporating the water or any other conventionalmeans.

[0024] It is also within the scope of this invention to deposit thedesired transition metal(s) from an organic (as opposed to aqueous)medium. Suitably the transition metal can be dissolved or suspended insuch medium, for example, as an organometallic compound, and thenimpregnated onto and into a suitable substrate. The organic carriermedium is removed, leaving behind the impregnated, deposited transitionmetal.

[0025] After the transition metal is combined with the substrate asaforesaid, it may be important to treat this combination so as toactivate it for this particular catalytic purpose, e.g., by heating itto separate the metal from other ligands, if any, in the depositioncompound. It may also be necessary to adjust the size of the preparedcatalyst to make it suitable for use in this invention. Comminution oragglomeration, e.g. by binding, may be desirable to produce particles ofthe proper size, i.e. of less than about 400 microns.

[0026] The catalyst of this invention may be put on the substrate hereofin any form or chemical oxidation state. It may be the oxide or havesome other ligand. It may be reduced prior to use, but this-is notnecessary since the fibril forming reaction is a reducing environmentand thus the transition metal will be reduced during, or immediatelyprior to, fibril forming use.

[0027] Fibrils which are very thin and long, diameters of about 3.5 to70 nanometers and L/D of up to 100 or more, are produced using thesecatalysts. These fibrils, as produced by this process, without thenecessity of further treatment, and without the coproduction of athermal carbon overcoat, comprise a carbon layer generally concentricabout an axis which comprises multiple essentially continuous layers ofordered carbon atoms, which preferably and usually are crystalline andgraphitic. This, as produced, outer layer of ordered carbon atoms oftensurrounds an inner layer of less ordered carbon atoms. Most preferredproducts of this invention are high yields of high quality, thin fibrilsof appropriate long length having substantially uniform, concentric,substantially continuous, ordered, multiple layers of carbon about anaxial (inner core) region, which has a differentcomposition/crystallinity and is preferably hollow. Such fibrilspreferably have up to about 100 times, and more greater length thandiameter, have diameters of up to about 700 angstroms and aresubstantially cylindrical graphite about a substantially hollow core asmade and without having been treated at higher temperatures than theoriginal fibril manufacturing temperature.

[0028] According to one apsect of this invention, operating withcatalyst particles as herein set forth, yields of fibrils of greaterthan about 30 times the weight of transition metal in the catalyst areachievable. In many cases, particularly with mixed transition metals,yields of between 100 and 200 times the weight of transition metal inthe catalyst have been achieved. It has been found that in comparableprocesses, combinations of transition metal catalysts have sometimesincreased yields by a factor of as much as 2 or even more.

[0029] The following examples illustrate the practice of this invention.By following one or more of these examples, high yields of uniquefibrils as above described are produced.

EXAMPLE 1

[0030] A catalyst was prepared using Degussa fumed alumina with anaverage particle size of about 100A and an aggregate mesh size of −100.Iron acetylacetonate was deposited on these alumina particles in a ratioof about 1 part iron, as the acetylacetonate, to 10 parts by weight ofalumina. The resultant particle was heated under a hydrogen/ethyleneatmosphere under reaction conditions.

[0031] A one (1) inch tube was heated to about 650° C. while it wasbeing purged with argon. A mixed flow of hydrogen, at 100 ml/min, andethylene, at 200 ml/min, was fed to the hot tube for five minuteswhereupon catalyst was introduced into the reactor tube. Theethylene/hydrogen mixture was continued through the tubular reactor for0.5 hours after which the reactor was allowed to cool to roomtemperature under argon. Harvesting of the fibrils so produced showed ayield of greater than 30 times the weight of the iron in the catalyst.

EXAMPLE 2

[0032] Into a 3 L. round bottom flask was added 80.08 g of Degussa fumedalumina and 285 ml of methanol. The mixture was stirred to produce athick paste before a solution of 78.26 g (0.194 moles) of ferric nitratenonahydrate and 4.00 g (0.0123 moles) of molybdenum(VI) oxidebis(2,4-pentanedionate) in 300 ml of methanol (Fe to Mo atom ratio of94:6) was added slowly. The thick paste which had collected on the sidesof the flask was washed down with 65 ml of additional methanol and themixture was stirred for 1 hour before house vacuum (28 in. Hg) wasapplied while stirring overnight. The purple-tinted solid was placed ina vacuum (28 in. Hg) oven at 100° C. for 29 hours. A total of 100.7 g ofcatalyst was obtained. The catalyst was ground and passed through an 80mesh sieve prior to use. Analysis of the catalyst indicated 9.43% byweight iron and 0.99% by weight molybdenum.

[0033] A vertical furnace containing a 1 inch quartz tube with aninternal quartz wool plug and thermocouple was equilibrated at 650° C.under a down flow of 100 ml/min. hydrogen and 200 ml/min. ethylene. Intothe tube (onto the quartz wool plug) was added 0.1044 g of theabove-described catalyst. After 30 min., the hydrogen/ethylene flow wasstopped and the oven was allowed to cool to near room temperature. Atotal of 1.2434 g of fibrils was harvested for a yield ratio of 126times the iron weight content of the catalyst.

EXAMPLE 3

[0034] A sample of catalyst from example 2 (1.6371 g) was placed in ahorizontal furnace under argon and was heated to 300° C. After 30 min.at this temperatrure, the furnace was cooled and 1.4460 g of catalystwas recovered (12% wt. loss), having 11.1% by weight iron and 1.2% byweight molybdenum.

[0035] A vertical tube furnace containing a 1 in. quartz tube with aninternal quartz wool plug and thermocouple was equilibrated at 650° C.under a 100 ml/min. down flow of hydrogen and 200 ml/min. down flow ofethylene. Into the hot tube was added 0.1029 g of the catalyst describedabove. After 30 min., the hydrogen/ethylene flow was stopped and theoven was allowed to cool to near room temperature under argon. A totalof 1.3750 g of fibrils was isolated for a weight yield based ontheoretical iron content of 120 times the iron content.

EXAMPLE 4

[0036] The vertical tube furnace described in Example 2 was equilibratedat 700° C. under the flow of 100 ml/min. hydrogen and 200 ml/min.propane. Onto the quartz wool plug was added 0.1041 g of catalyst fromExample 2. After 30 min. the fuel gases were stopped and the product wascooled under argon. A total of 0.3993 of fibrils was isolated for aweight yield of 41 times the catalyst iron content.

EXAMPLE 5

[0037] The procedure of Example 4 was followed at 650° C. using 0.1004 gof catalyst from Example 2. A total of 0.3179 g of fibrils was harvestedfor a weight yield of 34 times the iron content of the catalyst.

EXAMPLE 6

[0038] Into a round bottom flask was added 4.25 g of Degussa fumedalumina and 30 ml of methanol. The mixture was mechanically stirredwhile a solution of 4.33 g (10.7 mmol) of ferric nitrate nonahydrate and0.51 g (1.56 mmol) of molybdenum(VI)oxide bis(2,4-pentanedionate) in 50ml of methanol was slowly added. The mixture was stirred for 1 hourbefore the solvent was removed with the aid of a rotary evaporator. Theresulting damp solid was vacuum dried at 105° C., 28 in. Hg for 18hours. The resulting catalyst was ground and passed through an 80 meshsieve. A total of 5.10 g of catalyst was obtained. Analysis of thecatalyst indicated 9.04% by weight iron and 2.18% by weight molybdenumto be present.

[0039] Fibrils were prepared following the procedure of Example 2 at650° C. using 0.0936 g of the above catalyst. A total of 0.9487 g offibrils was isolated for a weight yield of 126 times the catalyst ironcontent.

EXAMPLE 7

[0040] Into a round bottom flask was added 3.80 g of Degussa fumedalumina and 30 ml of methanol. The mixture was mechanically stirredwhile a solution of 4.33 g (10.7 mmol) of ferric nitrate nonahydrate and2.04 g (6.25 mmol) of molybdenum(VI)oxide bis(2,4-pentanedionate) in 100ml of solvent was added. The mixture was held at 105° C. and 28 in. Hgfor 17 hrs. The dried catalyst was sieved (80 mesh) to produce 6.10 g ofpowder. Analysis of the catalyst indicated 8.61% iron and 8.13%molybdenum by weight.

[0041] Fibrils were prepared following the procedure of Example 2 at650° C. using 0.1000 g of the above catalyst. A total of 0.8816 g offibrils was isolated for a weight yield of 102 times the catalyst ironcontent.

EXAMPLE 8

[0042] The procedure of Example 7 was followed at 700° C. using methaneand 0.1016 g of catalyst. A total of 0.0717 g of fibrils was isolatedfor a yield of 8.2 times the iron content of the catalyst.

EXAMPLE 9

[0043] Into a 500 ml round bottom flask was placed 4.37 g of Degussafumed alumina and 28 ml of methanol. To the stirred mixture was added asolution of 4.33 g (10.7 mmol) of ferric nitrate nonahydrate and 0.46 g(1.32 mmol) of chromium acetylacetonate in 75 ml of methanol. Themixture was stirred for 1 hr. before it was dried for 18 hr. at 105° C.and 28 in. Hg. The catalyst was ground and sieved (80 mesh) to produce5.57 g of powder. The theoretical metal content by weight was 11.9% ironand 1.4% chromium.

[0044] Fibrils were prepared following the procedure of Example 2 at650° C. using 0.0976 g of the above catalyst. A total of 0.9487 g offibrils was isolated for a yield of 82 times the theoretical ironcontent.

EXAMPLE 10

[0045] Into a 500 ml round bottom flask was placed 4.40 g of Degussafumed alumina and 35 ml of methanol. To the thick paste was added 4.32 g(10.7 mmol) of ferric nitrate nonahydrate in 35 ml of methanol. Themixture was stirred for 45 min. before the solid was dried at 95° C. and28 in. Hg for 18 hr. The catalyst was ground and sieved (80 mesh).

[0046] Fibrils were prepared following the procedure of Example 2 at650° C. using 0.0930 g of the above catalyst. A total of 0.4890 g offibrils was isolated for a weight yield of 46 times the catalyst ironcontent.

EXAMPLE 11

[0047] Into a round bottom flask was placed 4.33 g of Degussa fumedalumina in 30 ml of methanol. To the stirred paste was added a solutionof 4.33 g (10.7 mmol) of ferric nitrate nonahydrate and 0.42 g (1.19mmol) of ferric acetylacetonate in 50 ml of methanol. The mixture wasstirred for 75 min. before drying at 105° C. and 28 in. Hg for 17 hrs.The solid was ground and sieved (80 mesh) to yield 5.87 g of catalyst.Analysis showed 13.79% iron present in the catalyst.

[0048] Fibrils were prepared following the procedure of Example 2 at650° C. using 0.0939 g of the above catalyst to produce 0.3962 g offibrils. This corresponds to 31 times the iron content of the catalyst.

EXAMPLE 12

[0049] Into a round bottom flask was added 4.33 g of Degussa fumedalumina in 20 ml of water followed by a solution of 4.33 g (10.7 mmol)of ferric nitrate nonahydrate and 0.17 g (0.138 mmol) of ammoniummolybdate in 40 ml of water. The mixture was mechanically stirred for 1hour. The water was removed at reduced pressure at 40° C. overnight.Final drying was accomplished at 140° C. and 26 mm. Hg for 21 hours toproduce 5.57 g of solid. Analysis of the catalyst showed 9.87% by weightiron and 1.45% by weight molybdenum to be present.

[0050] Fibrils were prepared following the procedure of Example 2 at650° C. using 0.0794 g of catalyst to produce 0.8656 g of fibrils. Thiscorresponds to 111 times the iron content of the catalyst.

EXAMPLE 13

[0051] Into a round bottom flask, containing 4.33 g of Degussa fumedalumina and 30 ml of methanol, was added a solution of 4.33 g (10.7mmol) of ferric nitrate nonahydrate and 0.16 g (0.368 mmol) of cericnitrate in 50 ml of methanol. An additional 20 ml of methanol was usedto wash all the salts into the flask. The mixture was stirred for onehour before the solvent was removed at reduced pressure. The solid wasdried at 130° C. and 27 mm Hg for four days to produce 5.32 grams ofcatalyst. Analysis of the solid indicated 9.40% iron and 0.89% cerium tobe present.

[0052] Fibrils were prepared following the procedure of Example 2 at650° C. using 0.0941 g of catalyst to produce 0.7552 g of fibrils. Thiscorresponds to 88 times the iron content of the catalyst.

EXAMPLE 14

[0053] Into a round bottom flask was added 4.33 g of Degussa fumedalumina and 30 ml of methanol. Onto the alumina was poured a solution of4.33 g (10.7 mmol) of ferric nitrate and 0.31 g (1.22 mmol) ofmanganese(II) acetylacetonate in 50 ml of methanol. The solvent wasremoved at reduced pressure (27 mm Hg) and the damp solid was vacuumdried at 140° C. to produce 5.18 g of solid. Analysis of the catalystindicated 9.97% iron and 1.18% manganese.

[0054] Fibrils were prepared following the procedure of Example 2 at650° C. using 0.070 g of catalyst to produce 0.4948 g of fibrils. Thiscorresponds to 66 times the iron content of the catalyst.

EXAMPLE 15

[0055] Into a round bottom flask was added 4.33 g of Degussa fumedalumina and 30 ml of methanol. Onto the alumina was poured a solution of4.33 g (10.7 mmol) of ferric nitrate and 0.43 g (1.22 mmol) ofmanganese(III) acetylacetonate in 50 ml of methanol. The solvent wasremoved at reduced pressure and the damp solid was vacuum dried at 140°C. to produce 5.27 g of solid. Analysis of the catalyst indicated 10.00%iron and 1.18% manganese by weight.

[0056] Fibrils were prepared following the procedure of Example 2 at650° C. using 0.0723 g of catalyst to produce 0.7891 g of fibrils. Thiscorresponds to 110 times the iron content of the catalyst on a weightbasis.

EXAMPLE 16

[0057] Degussa fumed alumina (400 g) and deionized water (8.0L) wereadded to a 22 L flask equipped with a stirrer, pH meter and probe, andtwo 2 L addition funnels One funnel contained an-aqueous solution offerric nitrate nonahydrate (511 g dissolved in 5654 ml of water) and theother an aqueous solution of sodium bicarbonate (480 g dissolved in 5700ml of water).

[0058] The pH of the alumina slurry was first adjusted to 6.0 by addingthe sodium bicarbonate solution to raise it or the ferric nitratesolution to lower it. Next, both solutions were added simultaneouslyover 3-4 hours with good agitation while maintaining the pH at 6.0. Whenthe addition was complete, stirring was continued for an additional ½hour, after which the slurry was filtered on a 32 cm Buchner funnel. Thefilter cake was then washed with deionized water and returned to the 22L flask. Next, additional deionized water was added and the slurrystirred for another ½ hour. The batch was then filtered, washed withdeionized water, and vacuum-dried at 100° C. to constant weight (475 g).Following drying, the final catalyst was prepared by grinding andsieving the product to −80 mesh.

EXAMPLE 17

[0059] This Example illustrates the practice of this invention usingperiodic addition of catalyst to produce high fibril yields. A four-inchquartz tube, closed on the bottom, was placed in a 4 inch diameter×24inch long furnace. The tube was purged with argon while being heated to620° C. When the tube was hot, the gas feed was switched to a mixture ofhydrogen (1.0 l/min) and ethylene (5.6 l/min) via a dip tube to thebottom of the 4 inch tube. After 5 min of purging, the catalyst additionwas begun.

[0060] A total of 41.13 g of catalyst, prepared as described in theExample 16, was added to the hot reactor reservoir. The catalyst wasadded periodically to the hot reactor in small portions (0.2 g) over aperiod of approximately 6 hours. After catalyst addition was complete,the reaction was allowed to run for an additional one hour and thereactor then cooled to room temperature under argon. The fibrils wereremoved from the tube and weighed. This batch gave 430 g total yield offibrils which is unusually high for a catalyst based upon iron has theonly transitionmetal. In single batch addition fo an iron only catalyst,fibril yields of about 30 times the iron content have been observedwhereas here the fibril yield is more than 70 times the iron content ofthe catalyst.

EXAMPLE 18

[0061] The tube and furnace described in Example 17 were heated to 650°under an argon purge. When the tube was hot the gas feed was switched tohydrogen and ethylene as described in Example 17.

[0062] A total of 20.4 g of catalyst (Fe—Mo) prepared as described inExample 2 was added in a manner similar to that described in Example 17.This batch gave a total fibril yield of 255 g.

1. In the process of producing carbon fibrils by decomposing a source ofcarbon at elevated temperatures in contact with a multivalent transitionmetal and recovering the fibrils formed thereby; the improvement,whereby increasing the yield of such fibrils, which comprises contactingsaid source of carbon at a temperature of about 500 to 1500° C. with acatalyst comprising at least one multivalent transition metal on aninorganic substrate having a size of up to about 400 microns, said metalbeing present on said substrate as a multiplicity of discontinuouscatalytic sites which, at least during fibril formation, have a size ofabout 35 to 700° A which size is measured by measuring the size oftransition metal particles recovered along with produced fibrils.
 2. Theimproved process claimed in claim 1 wherein said transition metalcomprises iron with a catalyst site size of about 60 to 300 A.
 3. Theimproved process claimed in claim 1 wherein said transition metal isiron mixed with at least one other transition metal.
 4. The improvedprocess claimed in claim 3 wherein said other transition metal is atleast one selected from the group consisting of molybdenum and chromium.5. The improved process claimed in claim 1 carried out at a temperaturebelow the thermal decomposition temperature of the carbon source.
 6. Theimproved process claimed in claim 1 wherein said carbon source is amixture of hydrocarbons.
 7. The improved process claimed in claim 1wherein said carbon source is at least one member selected from thegroup consisting of methane, ethane, propane, butane, benzene, butene,isobutene, cyclohexane, ethylene, propylene, acetylene, toluene, xylene,cumene, ethyl benzene, naphthalene, phenanthrene, anthracene,formaldehyde, acetaldehyde, acetone, methanol, ethanol and carbonmonoxide.
 8. The improved process claimed in claim 5 includingrecovering a high yield of product comprising long, thin fibrils which,as produced, comprise at least long portions consisting essentially ofordered carbon atoms as their outer layer.
 9. The improved process asclaimed in claim 1 carried out in an ebulliating bed wherein saidcatalyst/substrate has a particle size of about 50 to 300 microns. 10.The improved process as claimed in claim 1 carried out in a transportbed wherein said catalyst/substrate has a particle size of less thanabout 1 micron.
 11. The improved process as claimed in claim 1 includingcofeeding said catalyst/substrate and said source of carbon downflowthrough a reaction zone.
 12. The improved process claimed in claim 10including cofeeding said catalyst/substrate upflow through a reactionzone.
 13. The improved process claimed in claim 1 including cofeeding anon-hydrocarbonaceous gas with said carbon contributing feed.
 14. Theimproved process claimed in claim 1 including adding said catalystparticles to said process over the course of said fibril formingreaction.
 15. A process for producing high yields of long, thin fibrilscomprising at least long portions having atomically ordered outersurfaces, as made; which process comprises contacting a vaporous sourceof the atoms which will comprise said outer surface with a smallparticle substrate, having a size of up to about 400 microns and havingmultiple discrete catalytic sites comprising at least one transitionmetal, at a temperature of about 500 to 1500° C. but lower than thethermal decomposition temperature of said vaporous source of said atomsfor a time sufficient to form fibrils; and recovering a productcomprising said fibrils at least some of which have combined therewithat least one transition metal of a size of about 35 to 700° A.
 16. Aprocess as claimed in claim 15 wherein said vaporous source comprises amixture of a hydrocarbonaceous source of carbon and hydrogen.
 17. Aprocess as claimed in claim 16 wherein said transition metal comprisesiron, said hydrocarbonaceous source of carbon is ethylene and saidtemperature is about 600 to 900° C.
 18. A process as claimed in claim 16wherein said transition metal is iron and molybdenum.
 19. A process asclaimed in claim 16 wherein said transition metal is iron and chromium.20. A process as claimed in claim 16 wherein said transition metal isiron and cerium.
 21. A process as claimed in claim 16 carried out in afluidized bed.
 22. A long, thin carbonaceous fibril made up of at leastlong portions comprising, as made and without having been subjected totemperature higher than about 1500° C., an outer layer substantiallyconcentric about an axis consisting essentially of ordered carbon atoms.23. A fibril as claimed in claim 22 comprising a substantially hollowcore.
 24. A fibril as claimed in claim 22 comprising an inner layer ofcarbon less ordered than said outer layer.
 25. A multiplicity of fibrilscomprising at least some fibrils as claimed in claim 22 .